Orchard heater



Feb. 9, 1937. w. C. SCHEU I 2,070,142

ORCHARD HEATER Filed March 14, 1932 5 Sheets-Sheet 1' a X H i 12 24 X 6 22 41-. \QQ 0/ 3 .19 3

INVENT OR. W/L 4 /AM C.SCHEU,

Feb. 9, 1937. v w. c. s cHEu ORCHARD HEATER Filed March 14, 1932 3 Sheets-Sheet 2 I INVENTOR. j Will/9M Gar/ 0 M /7 M ARNEYS W. C. SCHEU ORCHARD HEATER Feb. 9, 1937.

3 Sheets-Sheet 3 Filed March 14, 1932 INVENTOR. WILL/AM CSCHE U, M K

A TTORNEYS Patented Feb. 9, 1937 UNITED STATES Z,70,l4.?; PATENT OFFIQE ORCHARD HEATER Application March 14, 1932, Serial No. 598,741

9 Claims.

This invention relates to liquid fuel heaters adapted for orchard heating and particularly to an orchard heater having an improved form of combustion housing.

The invention further relates to a combustion housing adapted for use with a liquid fuel heater of conventional construction, providing an improvement in the combustion features of said heater.

The principal object of this invention is to provide an orchard heater having an improved form of combustion housing adapted to effect a superheating of the combustible fuel vapors entering said housing, prior to the actual combustion of such vapors, whereby the combustion efliciency of the heater is materially improved.

A further object of the invention is to provide improved means for combustion of the previously heated vapors.

A particular object of the present invention, in its preferred embodiment, is to provide an orchard heater of the above described type wherein the heated vapors aforesaid are caused to enter the combustion housing at points adjacent the lower portion thereof and caused to rise in said housing, preferably with a rapidly increasing velocity, to a higher level spaced upwardly from said points of entrance, and wherein combustion air is admitted to said combustion housing at a point below the point of entrance of said heated vapors and also at a point adjacent said higher level, whereby, due to the high velocity of said heated vapors in passing said second-named point of air admission, substantially complete combustion of said vapors is subsequently obtained adjacent this point and in the upper portion of the combustion housing, producing a minimum quantity of unburned carbon in the form of soot in the exit gases.

A further object of this invention is to provide a liquid fuel orchard heater provided with a combustion housing having improved means whereby the inner walls thereof may be easily cleaned of any adhering substances such as soot.

Further objects of the invention will be brought out in the following description or will be apparent therefrom.

The orchard heater combustion housing of the present invention is adapted to be placed or used upon a heater base portion of any suitable type provided with a fuel storage receptacle and with air admitting means for effecting vaporization of such fuel. Such vaporization is ordinarily obtained by means of a relatively small vaporizing flame maintained in said heater base portion which heats and vaporizes the fuel, and the vapors so produced pass upwardly into the combustion housing.

An important feature of this invention consists in the provision of a Vapor heating means within the combustion housing, so arranged as to be heated by the combustion within said housing and adapted to receive the fuel vapors formed as above described and heat the same before delivering the same into contact with air for supporting the main combustion operation. The combustion housing comprises a lower portion surrounding the vapor heater and an upper portion or stack extending upwardly above the upper end of the vapor heater. The lower portion of the combustion housing is formed as an outer housing of somewhat larger diameter than the vapor heater, providing an annular space therebetween which serves as a mixing and combustion chamber. The vapor heater has openings leading from the interior thereof into the lower portion of said annular space, and the combustion housing is also provided with means for admitting air to said space. A portion of this air is preferably admitted. upwardly through openings in the bottom of the combustion housing, and additional air is preferably admitted through openings in the side of the outer housing adjacent the level of the upper end of the vapor heater, that is, at the upper portion of said space. The vapor heater is preferably disposed substantially centrally within said combustion housing, and serves the further purpose of spreading the vapors outwardly into position to contact air admitted to said annular space and causing the combustion in the lower part of the combustion housing, around and immediately above the vapor heater, to be confined to a region close to the side walls of the combustion housing.

The side walls of the outer housing and the vapor heater preferably converge upwardly toward one another so that the lower portion of the space between said outer housing and said vapor heater is of larger cross-sectional area than the upper portion of said space, whereby the vapors entering the lower portion of said space from the vapor heater are caused, due to the convergence of the space, to accelerate in their passage upwardly through said space. This feature provides a relatively high velocity of the vapors past the upper openings through which air is admitted to said space, obtaining through intermixing of the vapors and air. The upper portion of the combustion housing is formed as a stack extending upwardly from said outer housing, said stack being of much greater crosssectional area than any portion of the space between the vapor heater and the outer housing and the velocity of gas travel therethrough is correspondingly less, which feature allows the gases to burn within said stack until combustion is substantially complete, materially decreasing the possibility of any unburned portions of fuel vapors being discharged into the atmosphere and chilled. This feature has been found to provide substantially complete combustion at even high rates of fuel consumption, producing exit gases which are remarkably free of unburned carbon or soot.

Under some conditions of operation of the heater, namely, when starting the heater, some soot may sometimes be deposited in the space between the vapor heater and the outer housing while the heater is warming up. For the purpose of effecting easy removal of such accumulated soot I provide suitable scraper or brush means rotatably disposed within said outer housing whereby said soot may be scraped from the walls and shaken through the air admitting openings in the bottom of the combustion housing, when desired.

The invention may be considered as comprising a combustion housing provided with vapor heating and combustion producing means as above described, adapted to be mounted on any suitable type of combustible vapor generating means, or it may be considered as comprising a complete orchard heater including a base portion adapted to contain liquid fuel and provided with air admitting means for vaporizing such fuel, with said combustion housing mounted thereon.

Several embodiments of my invention are illustrated in the accompanying drawings, and referring thereto:

Fig. 1 is a vertical section of a preferred embodiment of the invention, showing a complete heater of my invention;

Fig. 2 is a transverse section thereof on line 22 in Fig. l, with the cover of the base section removed;

Fiig. 3 is a transverse section thereof on line 33 in Fig. 1;

Fig. 4 is a transverse section thereof on line iin Fig. 1;

Fig. 5 is a vertical section of a modified form of the combustion housing, provided with an alternative form of vapor heater;

Fig. 6 is a vertical section of another modified form of the invention, showing an alternative form of construction which may be employed;

Fig. '7 is a vertical section of another modified form of combustion housing, embodying an alternative form of stack, and also showing alternative forms of other parts, as hereinafter described.

The form of invention shown in Figs. 1 to 4 may comprise a heater base portion 5 consisting of a fuel receptacle 2 and a cover 3, said fuel receptacle being provided with baffie means 4 secured to the side wall of said receptacle in any suitable manner, as for example, by means of a hook 5 at the outer upper edge of said baifle, said hook being engaged by a loop 5 secured to the said side wall. The baffle may be of any desired type, the form shown being merely typical and comprising two side walls to and 6b and an outer wall 40, said walls Ala and 4b being sloped inwardly of the heater, as shown.

The cover of the heater base portion is provided with suitable air admitting means whereby a regulated quantity of air may be admitted to the heater base for the purpose of maintaining a vaporizing flame directed downwardly toward the surface of the liquid fuel within the receptacle, whereby the fuel is heated and combustible vapors evolved therefrom. Any suitable type of air admitting means may be employed and for purposes of description I show means such as indicated at 6 provided on the cover 3 inwardly of the outer edge thereof. Said air admitting means is shown as comprising an opening 6a in the cover, a cap member Eb hingedly mounted on the cover at 'i. and fitting around the edges of the opening Ba, said cap member being mounted for pivotal movement about a hinge axis lying substantially parallel to the plane of said opening, and plate 5a pivotally mounted as at 81) on said cap member. A plurality of openings 60 are provided in the cap member 62) and an are shaped opening 8c in plate 8a is adapted to be moved into or out of position of partial or total alignment with one or more of said openings 60 up on rotation of the plate 8a. The plate 8a may be provided with a handle 9 for rotation thereof to regulate the exposed area of the openings to.

In addition to the above mentioned vaporizingflame air-admitting openings the apparatus may be provided, if desired, with a plurality of suitable air inlet holes or openings 3b in the cover 3 for the purpose of admitting relatively small amounts of atmospheric air to the interior of the heater, which air will be mixed with the vapors liberated from the fuel and will be carried upwardly therewith. In this manner, the combustible vapors may be rendered somewhat more easily ignited upon contact with air for the support of combustion, as subsequently described. It will be understood that any of the subsequently described forms of apparatus may be provided with the above-mentioned openings 3b, if desired.

The combustion housing of the present invention may comprise a vapor heater H communicating with the interior of the fuel receptacle 2, a lower portion or outer housing l2 surrounding the vapor heater and an upper portion or stack extending upwardly from said outer housing above the upper end of the vapor heater. The vapor heater shown in the present form of device is formed as an inverted truncated hollow cone provided with a cylindrical depending collar 14 adapted to fit within a circular opening I5 in the cover of the heater base portion. A plurality of openings 56 are provided in the side walls Ila of the vapor heater, adjacent the lower end thereof, communicating with the surrounding space defined by the outer housing 12. The upper end of the vapor heater is closed by a wall Hb, upon which is provided a suitable handle ll. The outer housing I2 is substantially cylindrical in shape, and the combustion housing is provided with a radial bottom wall l8 having a centrally disposed depending flange l9 adapted to receive the upwardly projecting flange or collar 3a defining the central opening H5 in the heater base cover 3. Suitable openings 2| are provided in the bottom wall l8 of the housing, through which air for support of combustion may be admitted.

The outer housing l2 is further provided with air inlet means disposed adjacent the upper end thereof, there being shown two rows of slots 22 and 23 for this purpose, the slots of each row overlapping and being overlapped by the slots of the other row. This form of air inlet openings has been found to have a very high combustion efiiciency by virtue of the admission of a large quantity of air in a plurality of relatively narrow streams, whereby a very uniform mixture of air and combustible gases is obtained. The flared side walls of the vapor heater, together with the side walls of the outer housing l2 define an annular space A of upwardly decreasing cross-sectional area surrounding said vapor heater, said space being of relatively large cross-sectional area at the lower portion thereof and of relatively small cross-sectional area at the upper portion thereof adjacent the slots 22 and 23, forming a constricted annular throat B.

Means are also provided for removing or dislodging deposited soot or carbon from the side walls of the outer housing l2 and from the bottom wall l8, and such means may comprise a plurality of scrapers 24 secured to the side walls Ila of the vapor heater II and adapted to scrape the inner side walls of the outer housing l2 and the bottom wall l8 upon rotation of the vapor heater with respect to said walls by means of the handle IT. The scrapers may be of any suitable type, the form shown in Figs. 1, 3 and 4 comprising a strip of strap iron or the like secured to the side wall of the vapor heater as at 25, rotatable therewith, and shaped to conform to the shape of the walls l2 and I8. Any soot or the like scraped from the walls is allowed to fall out through the openings 22 in the bottom walls 18. If desired, the scraping means may comprise a construction such as shown in Fig. '7, comprising a plurality of wire brushes or the like, 24a, disposed on arms 24b secured to the vapor heater II.

The combustion housing upper portion or stack defining the combustion space C may comprise a substantially cylindrical section l3 provided with a bead 26 adjacent the lower edge thereof adapted to rest upon and be supported by the upper edge of the outer housing l2 and in tight engagement therewith, a reducing collar 21 and an upper portion l3a of smaller diameter than the portion I 3. The stack is preferably provided with a portion 28 depending from the bead 25 in such manner as to cover the slots 22 and 23 and prevent access of wind and rain thereto, and the collar 21 is preferably provided with a depending positioning flange 21a. The upper stack portion |3a is also preferably provided with a removable lid or cover 3| at the upper end thereof. The stack may be provided with a flame baflie 29 pcsitioned centrally with respect thereto at the lower end of the upper stack portion l3a;, if desired, said baflle being secured in any suitable manner to the collar 21. This baffle obtains a partial confinement of the burning gases within the combustion space C, providing for optimum heating of the vapor heater II. If desired, the outer housing l2 may be provided with lugs [2a secured to the walls thereof at suitable intervals on the periphery, for the purpose of positioning the stack l3 by engagement with the portion 28,

as shown. i

If desired, the stack portion l3 may be extended upwardly to a greater height as shown at 3 in Fig. '7, and the upper stack portion l3a of reduced diameter may be dispensed with. This form of stack is preferably provided at its upper end with a reducing collar 21' provided with a hinged cover 3| over the central opening 27, whereby the entire stack l3 may be opened by removing the collar 21', or, the cover 3| may be laid back, opening only the opening 21".

The modification of the combustion housing shown in Fig. 5 may comprise a substantially cylindrical vapor heater 38 having its upper end closed by a wall 38a and provided with openings 39 in the side walls thereof after the manner of the openings l5, Fig. 1, and the side walls of the outer housing 4| surrounding said vapor heater are preferably sloped inwardly and upwardly as shown so as to form an annular space A of upwardly decreasing cross-sectional area between said walls and said vapor heater.

The converging side walls of the outer housing 4|, together with the vapor heater, form an annular space comparable with that shown in Fig. 1, of relatively large cross-sectional area at the lower portion and of relatively small cross-sec tional area at the upperportion, forming a throat B. The outer housing is preferably provided with a plurality of air admitting openings adjacent the level of the throat B, which may be of the type shown in Fig. 1, comprising slots 42 and 43 arranged in over-lapping fashion. The combustion housing is further provided with openings 44 in the bottom wall Ala, after the manner of the openings 2|.

The stack may comprise a cylindrical portion 45 provided with a shoulder 46 adapted to be supported on the upper edge of the outer housing 4!,

and a depending collar 4'! flared outwardly from a the shoulder 46 adapted to serve as a shield for the openings 42 and 43. The device may be provided with scraper means, if desired, such as is shown at 48 secured to the vapor heater 3B and adapted, by engagement with the bottom wall a i a, to support said vapor heater in position within the outer housing 4|. The vapor heater may also be provided with a suitable handle 38b whereby said vapor heater may be rotated relative to the outer housing A! for operation of the 1 scraper means 48.

The combustion housing shown in Fig. 5 may be provided, if desired, with any suitable form of cover for the upper end of the stack, such as shown in Fig. l or in Fig. 6.

The form of invention shown in Fig. 6 may comprise a heater base portion 63 having a cover 64 and adapted to contain a liquid fuel to a suitable level such as indicated at L. The cover 64 is provided with air admittingmeans 65 for maintaining a vaporizing flame within the base portion, and a central opening 66 defined by a vertically extending flange 61. The vapor heater and combustion housing are adapted to be sup ported Within and without the flange 61, respec- 4.;

tively. A cylindrical tubular member 58 extends downwardly from the vapor heater into the base portion 63 through the central opening 66 and is provided with vertical slots or elongated openings 69 for passage of fuel vapors from the base .i?

portion 63 into said cylindrical member, said cylindrical member being adapted to serve as a vapor baffie to prevent flashing of the vaporizing flame from beneath the air admitting means 55 upwardly into the combustion housing. The va- 5-" por heater may comprise a hollow inverted frusto-conical portion H provided with a top Wall Ha and vapor outlet openings 72 in the lower portion of the side walls thereof, corresponding to the openings l6, Fig. 1.

The outer housing may in this case comprise a plurality of circular sections 13, M and 15 spaced from one another to provide annular air inlet openings 16 and Ti therebetween, as shown. The

lower section F3 is preferably provided with a '1.-

depending collar 13a adapted to fit over the flange l on the cover 64 and is further provided a bottom wall 18 having a plurality of air inlet openings 18a, allowing admission of air to the space between the vapor heater and the outer housing, m

below the level of the vapor inlet openings I2. The several cylindrical housing sections are inter-supported in any suitable manner as, for example, by means of spacing bolts 19 and 19a.

The middle section '54 is preferably of frusto- 75 conical shape, as shown, so that the general shape of the housing may provide an annular space of upwardly decreasing cross-sectional area around the vapor heater, as above described, the lower portion of said space or chamber being of relatively large cross-sectional area, as at A and the upper portion of said space comprising a throat B" of relatively small cross-sectional area adjacent the upper level of air admission, at opening ll. The stack portion of the combustion housing may comprise a frustoconical member 8! provided with a shoulder 82 adapted to be supported upon the upper edge 15a of the upper section "E of the outer housing. The stack is shown in this case as provided with a hinged cover 83, hingedly secured at M to the upper end of member 85 and adapted to be swung away from over the stack, to some such position as shown in dot-and-dash lines at 35.

In the operation of the heater 0f the present invention, the liquid fuel in the heater base portion is heated by means of the vaporizing flame maintained beneath the air admitting means in the cover of the heater base portion, and the fuel is thus caused to produce combustible vapors which rise into the vapor heater and are supereated therein. The vapors pass from the vapor heater into the annular space between the vapor heater and the outer housing, and are contacted by atmospheric air and combustion caused to take place. When the apparatus provided with air admitting openings of the type-shown at 31) in Fig. 1, the air admitted through these openings is mixed with the vapors passing into the vapor heater and is also heated therein. The

admission of air in the above manner allows of very smooth and uniform operation of the heater as combustion of the heated vapors within the combustion housing is facilitated by said vapors being relatively easily combustible due to the presence of the admixed and preheated air.

Referring to Fig. 1, for example, partial combustion is obtained in the annular space A from contact of the vapors with air admitted through the openings 2 l, and the partially burned vapors, together with the products of partial combustion are caused to rise in the space A and are mixed with additional atmospheric air in the throat B, such additional air being admitted through the slots 22 and 23. The main combustion of the vapors occurs in the space C above the vapor heater H. The combustion in the annular space A and in the combustion space above the vapor heater ii provides for maintainthe vapor heater at a temperature suitable for heating of the vaporized fuel prior to contact thereof by atmospheric air. It will be seen that due to the relative configuration of the outer housing walls and the vapor heater walls, the vapors are caused to pass through the throat B at a considerable velocity, obtaining an optimum intermixing of the vapors and combustion air.

The device of the present invention thus comprises means for heating the combustible vapors before intermixing the same with the com bustion supporting air, and provides novel means for causing the combustible vapors to be mixed with combustion air and enter the main combustion zone at a high velocity, so that the comnstion is obtained under optimum conditions.

It will be understood that any suitable form of stack may be provided for the device, said stack being of such length and shape as to provide for the desired amount of draft, and also, preferably of sufficiently large cr'oss-sectionalarea that the rate of passage of the gases therethrough allows of sufiicient time for the substantially complete combustion thereof during such passage.

The heater of the present invention is adapted to be lighted in the conventional manner, that is, by introduction of a burning lighting liquid into the interior of the combustion housing through the upper end thereof, and also into the fuel receptacle through the air admitting means such as at 6'. 'The burning liquid introduced into the combustion housing serves to heat the walls thereof and the vapor heater, while the burning liquid introduced into the fuel receptacle serves to start the vaporizing flame beneath the air admitting means and produce combustible vapors which pass through the vapor heater and are subsequently ignited and burned in the combustion housing.

I claim:

1. A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and'spaced from said vapor heater side wall; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said outer housing side wall and said vapor heater side wall being so formed as to define therebetween an annular chamber of upwardly decreasing cross-sectional area; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with the lower portion of said annular chamber; said outer housing being provided with openings for admitting air to said annular chamber; and the interior of said stack portion communicating with the upper end of said annular chamber.

2. A combustion housing for an orchard heater as set forth in claim 1, said vapor heater side wall being of inverted frusto-conical shape and said outer housing side wall being substantially cylindrical in shape.

3. A combustion housing for an orchard heater as set forth in claim 1, said vapor heater side wall being substantially cylindrical in shape, and said outer housing side wall being of frusto-conical shape.

4, A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding andspaced from said vapor heater side wall to define therebetween an annular chamber; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with said annular chamber; said combustion housing having openings for admitting air into the lower portion of said annular chamber adjacent the position of said vapor outlet openings, and said outer housing side wall having openings at its upper portion for admitting air into said annular chamber adjacent the level of the upper end of said vapor heater; and the interior of said stack portion communicating with the up er end of said annular chamber, at least one of said first-mentioned and last-mentioned side walls converging upwardly toward the other side wall in such manner that the cross-sectional area of said annular chamber decreases upwardly to a minimum area adjacent the upper end of said vapor heater, and the air admitting openings at the upper portion of said outer housing side wall being located adjacent the level of said minimum cross-sectional area of said annular chamber.

5. A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and spaced from said vapor heater side wall to define therebetween an annular chamber; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with said annular chamber; said combustion housing having openings for admitting air into the lower portion of said annular chamber adjacent the position of said vapor outlet openings, and said outer housing side wall having openings at its upper portion for admitting air into said annular chamber adjacent the level of the upper end of said vapor heater; and the interior of said stack portion communicating with the upper end of said annular chamber, said vapor heater side wall being of inverted frusto-conical shape and said outer housing side wall being substantially cylindrical in shape, whereby the crosssectional area of said annular chamber decreases upwardly to a minimum area adjacent the upper end of said vapor heater, and the air admitting openings at the upper portion of said outer housing side wall being located adjacent the level of said minimum cross-sectional area of said annular chamber.

6. A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and spaced from said vapor heater side wall to define therebetween an annular chamber; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with said annular chamber; said combustion housing having openings for admitting air into the lower portion of said annular chamber adjacent the position of said vapor outlet openings, and said outer housing side wall having openings at its upper portion for admitting air into said annular chamber adjacent the level of the upper end of said vapor heater; and the interior of said stack portion communicating with the upper end of said annular chamber, said vapor heater side wall being substantially cylindrical in shape, and said outer housing side wall being of frusto-conical shape, whereby the cross-sectional area of said annular chamber decreases upwardly to a minimum area adjacent the upper end of said vapor heater, and the air admitting openings at the upper portion of said outer housing side wall being located adjacent the level of said minimum cross-sectional area of said annular chamber.

7. A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and spaced from said vapor heater side wall to define therebetween an annular chamber; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with said annular chamber; said combustion housing having openings for admitting air into the lower portion of said annular chamber adjacent the position of said vapor outlet openings, and said outer housing side wall having openings at its upper portion for admitting air into said annular chamber adjacent the level of the upper end of said vapor heater; and the interior of said stack portion communicating with the upper end of said annular chamber, said air admitting openings at the upper portion of said outer housing comprising at least two circumferential rows of vertically elongated, uniformly spaced slots, the respective rows being at different levels but overlapping one another and the slots in the respective rows being arranged alternately in such manner that the upper ends of the slots in a lower row overlap and extend between the lower ends of the slots in a higher row.

8. A combustion housing for an orchard heater c mprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and spaced from said vapor heater side wall to define therebetween an annular chamber; a stack portion extending upwardly from said outer housing above the level of said vapor heater; said vapor heater being rotatably disposed with respect to said outer housing; and scraper means secured to said vapor heater and rotatable therewith in scraping contact with the interior of said outer housing side wall; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with said annular chamber, and said outer housing being provided with openings for admitting air to said annular chamber.

9. A combustion housing for an orchard heater comprising a vapor heater having an opening at its lower end to receive fuel vapor and having a side wall and a top wall closing the upper end thereof; an outer housing having a side wall surrounding and spaced from said vapor heater side wall to define therebetween an annular chamber; and a stack portion extending upwardly from said outer housing above the level of said vapor heater; said outer housing side wall and said vapor heater side wall being so formed as to define therebetween an annular chamber of upwardly decreasing cross-sectional area; said vapor heater side wall being provided at its lower portion with vapor outlet openings communicating with the lower portion of said annular chamber; said outer housing side wall being provided with air admitting openings in the upper portion thereof adjacent the level of minimum cross-sectional area of said annular chamber; said stack portion being supported upon the upper edge of the outer housing side wall and in tight engagement therewith and defining a main combustion chamber above said vapor heater communicating with the upper end of said annular chamber, and said stack portion having a depending collar extending downwardly around and spaced from said outer hou...- ing side wall to a level below said air admitting openings in said last-named side wall.

WILLIAM C. SCHEUT. 

